There's a lot more to it than just adding the song files. You have to unpack the arc files to access the musicDB, add the song info manually, enter the correct ID, then pack the arc file again. If you mess up even one thing, the game will break. It's not worth the trouble. Again, use Stepmania.
Please read though the outdated A20 thread for additional hints and download links for the tools you need. We're not here to spoon-feed you answers.